Paul, the son of Rep. Ron Paul, R-Texas, beat Kentucky Secretary of State Trey Grayson for the Republican nomination to run in November for the Senate seat open by the retirement of Republican Sen. Jim Bunning. With 43 percent of the precincts reporting, Paul led Grayson by 60 percent to 36 percent.

Paul's victory represented a defeat for Kentucky's Republican hierarchy, which solidly backed Grayson. Kentucky's powerful senior senator, Minority Leader Mitch McConnell put his weight behind Grayson, as did former Vice President Dick Cheney, who called Grayson the real conservative in the race.

Paul, however, had tea party support and the backing of former vice presidential candidate Sarah Palin, a movement favorite, and from Bunning, who has strained relations with McConnell and other state Republicans.

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In a statement, McConnell said that Paul "ran an outstanding campaign which clearly struck a chord with Kentucky voters and I congratulate him on his impressive victory. Now Kentucky republicans will unite in standing against the overreaching policies of the Obama Administration."

In Kentucky, Pennsylvania and Arkansas, voters were showing a willingness to buck Republican and Democratic party loyalty to eat their own, much in the way Utah's Republican Party convention earlier this month rejected conservative Sen. Bob Bennett's bid for a fourth term and West Virginia Democratic voters ousted 14-term Rep. Allan Mollohan in that state's primary last week.

Specter, an 80-year-old five-term incumbent, was hoping his switch from Republican to Democrat and the backing of President Barack Obama, Gov. Ed Rendell and the AFL-CIO would push him over Rep. Joe Sestak, D-Pa., and put him on a path to face former Rep. Pat Toomey, R-Pa., in November's general election.

Sestak was viewed more as an irritant than an obstacle to Specter running for a sixth Senate term. However, the 58-year-old two-term House member and retired Navy three-star admiral managed to erase a double-digit deficit to pull into a dead heat with Specter in the days leading to the primary.

White House Press Secretary Robert Gibbs said Monday that Obama hasn't followed the Arkansas and Pennsylvania Senate contests that closely, even though Obama cut a radio ad for Specter last month and Vice President Joe Biden personally campaigned for the senator.

In Arkansas, Lincoln, 49, a two-term centrist incumbent, was campaigning hard to win over 50 percent of the vote against state Lt. Gov. Bill Halter to avoid a runoff election, but a third Democrat in the primary could complicate those efforts.

Lincoln was thought to be the most vulnerable candidate prior to the primary. Lincoln angered Democratic liberals and labor organizations with her moderate voting record. She was one of the last Democratic holdouts in November on a crucial test vote that kept the health care bill alive, but in March, was one of three Senate Democrats to oppose the bill on final passage.

However, as the chairman of the usually little-noticed Senate Agriculture Committee, she could have influence over the next major bill: Financial regulatory overhaul.

Her committee has jurisdiction over regulating derivatives, the complex financial instruments that contributed to the 2008 economic collapse. She steered through her committee an approach that was tougher than that pushed by Senate Democratic — and liberal — leaders, a plan that would require big banks to spin off their lucrative derivatives practices into free-standing subsidiaries.

While that helped her assert herself as a champion of the consumer, she also was helped by two other factors: Strategic voting and her personality.

"Even liberal Democrats started to do some political calculus and think in a strategic way,' said Arkansas Poll Director Janine Parry. "They began to wonder whether Halter could win the general (election)."

MoveOn.org, a group friendly to Democrats, proudly reported Tuesday that more than 50,000 of its members gave nearly $2 million to Halter's campaign. The group also supported Sestak over Specter.

"These men are not afraid to fight for the progressive principle that democracy should work for all Americans not just those who can buy access or those who have a direct line into Washington, D.C.," said Ilyse Hogue, MoveOn.org's director for political advocacy and communications.

(Douglas reported from Philadelphia; Abdullah and Lightman reported from Washington.)